By performing Samyama on
the relation between Akasa and the ear, super physical hearing. (III-42)

Each of us as human being operates in a frequency range of sound (20 cycles per sec to 20,000 cycles per sec.) beyond which we do not hear. This is called the ahata sabda (audible range). The sound beyond, the anahata sabda (inaudible range) could cause either growth or deterioration. Those sounds, which bring growth, come under the heading of "divyam srotram". The humming resonating sound of the temple bell or the special sounds of the 'OM' sound are examples of these divine sounds heard in the subtler layers of mind coming as if from outside.

Hearing of such sounds are milestones of progress in the journey of yoga and spirituality.